Field of the Invention
The present invention relates to a solid-state imaging device and an imaging system.
Description of Related Art
In recent years, imaging systems, such as a video camera and an electronic still camera, have become widespread. In these imaging systems, a charge coupled device (CCD) solid-state imaging device or a complementary metal oxide semiconductor (CMOS) solid-state imaging device is mounted. In these solid-state imaging devices, a plurality of pixels are arranged in a two-dimensional matrix, and a signal charge generated by a photoelectric conversion unit, such as a photodiode, provided in a pixel, on which light is incident, is amplified by an amplification unit provided in the pixel and is output as a pixel signal. At this time, in a general CMOS solid-state imaging device, hitherto, the pixel signals from the pixels arranged in a two-dimensional matrix have been sequentially read for each row.
A CMOS solid-state imaging device can be manufactured using a general semiconductor manufacturing process while a CCD solid-state imaging device is manufactured by a dedicated manufacturing process. From this, the CMOS solid-state imaging device easily realizes multifunctionality by various functional circuits being incorporated into a solid-state imaging device, like a system on chip (SOC). For this reason, in a CMOS solid-state imaging device (hereinafter, referred to as a “solid-state imaging device”) mounted in an imaging system, there are an increasing number of examples where a solid-state imaging device has an internal analog-to-digital conversion circuit and pixel data obtained by performing analog-to-digital conversion on the pixel signals read from the pixels is output.
With recent increases in the speed of solid-state imaging devices, a transfer rate of pixel data between a solid-state imaging device in an imaging system and an image processing unit has been improved. In solid-state imaging devices, it is known that an improvement of a data transfer rate is coped with by improving a clock frequency when transferring pixel data to be output corresponding to a low voltage differential signaling system (LVDS), which is a differential interface system, or by increasing the bus width of a data bus for transferring pixel data to an image processing unit.
However, if the clock frequency in transferring pixel data from the solid-state imaging device to the image processing unit increases or the bus width of the data bus increases, the power consumption of the solid-state imaging device also increases. For this reason, a conventional general solid-state imaging device is provided with a mechanism for changing the number of bits of pixel data of one pixel (see Japanese Unexamined Patent Application, First Publication No. 2009-182412).
In an imaging system in which a solid-state imaging device provided with a mechanism for changing the number of bits of pixel data is mounted, the number of bits of pixel data transferred from the solid-state imaging device to the image processing unit is changed according to the operation mode of the imaging system. For example, in a case where the operation mode of the imaging system is a still image mode for capturing a still image, 12-bit pixel data is transferred from the solid-state imaging device to the image processing unit, and in a case of the operation mode for capturing a moving image, 10-bit pixel data is transmitted from the solid-state imaging device to the image processing unit. Furthermore, for example, in a case where the operation mode of the imaging system is a live view mode for displaying a confirmation image (a live view image (through image)) for confirming an object to be imaged on a display device, 9-bit pixel data is transferred, whereby the number of bits of pixel data transferred from the solid-state imaging device to the image processing unit is further reduced.
In this way, in an imaging system in which a solid-state imaging device provided with a mechanism for changing the number of bits of pixel data is mounted, the number of bits of pixel data transferred from the solid-state imaging device to the image processing unit is changed according to the operation mode, thereby reducing the power consumption of the solid-state imaging device and the imaging system.